Telephone receiver



Dec. 1941- P. N. ROSEBY 2,266,515

TELEPHONE RECEIVER Filed Sept. 25, 1939 INVENTOR. PHIL/P NORTON ROSE BY ATTOR/VE).

but of course applicable the effect of the the receiver. This has,

' to say, the' magnet maybe Patented Dec. 1a, 1941 UNITE.

p rnmrnonaancnrvaa "Philip uomn-nosebbwoodvde.nearsoutapm,1 Associated England, assignor to Telegraph Company, tionoi' Delaware Application September-25,1939, sen-.1 more Britain September 2s.-

Tclephone 1&1

Chicago. 111., acorpora- No. 296.415" 7 193a a The" present invention is concerned with 1111- provements in or relatin to receivers i'or' audio currents commonly referred to as telephone receivers because of their general use in telephony, to receiving electrical currents of any kind capable of giving an audible signal. Such receivers as is well-known, commonly include a permanent magnet system and permanent magnet is to create a magnetic field which extends beyond thereceiver and may 'deleteriously' effect instruments. or the like in its neighbourhood. In order to overcome this disadvantage it has been proposed to provide an iron case completely surrounding among others, the disadvantage that it makes the receiver unduly heavy.

An object of the present invention is to overcome this disadvantage in a more efllcient manner while at the same time considerably reducing the weight of the receiver.

Fig. 1 is a plan view oi a receiver according to the'invention. #1 1 2'is a. cross section .oiathe receiver.

Figs. 3 and 4am plan and elevationrespectively ot-a pole piece or the receiver.

. The telephone receiver has a casing I which may be of moulded insulating material. In addition there is an inset easing 2 whichmay be of aluminium or other similar light metal. The receiver cap of similar material to the casing is shown in Fig. 2 in two embodiments 3 and 3'. The embodiment 3 is provided with Openings 4 for the free egress ofmoisture. The diaphragm l is clamped between the casing and cap in the normal manner. Inside the inset casing 2 there is provided a thin annular ring 6 of soft iron 10- One of the features of the invention to attain this end is the employment of a small bar magnet of material specially capable of withstandin self-demagnetisation so that it can be employed in short lengths, for instance, that known under the registered trade-mark Alnico,"--which islanalloy of aluminium, nickel and cobalt in place of the usual C-shaped, ring-shaped or horse-shoeshaped permanent magnet of tungsten steel or like material whichnecessitates a'comparatively long length of magnet to ensure the retention or the strength of the magnet.

The second. feature of the present invention is the employment of a casing of aluminium or similar light material having insets 'of iron sheeting so as to completely surround the magnetic system other than at the end at which the diaphragm is located,,the diaphragm itself serving to act as a shield as well as to perform its normal fucntion. 'In order to assist in the reduction of stray magnetlc fields an auxiliary magnet is located in the casing in appropriate relationship to the bar magnet so as to act in a similar way to the second magnetin .an astatlc galvanometer, that is bar-shaped and arranged parallel and at some distance from the main bar magnet end having its poles of opposite polarity, the position being so chosen as to'have the minimum effect upon the flux of the permanent magnet which reaches the diaphragm while with a maximum effect upon the stray'flux.

The invention will be better understood by referring to the following description in conjunction with the accompanying drawing.

. rests on the inset casing ll shown in ing 24 in the casings.

'ter is a rectangular bracket into which fits ther bar magnet cated against the sides of the casing andserving as a magnetic shield torthose sides. A further thin soft iron disc I is also provided located in the face of the casing the inset casing 2. This is also for screening purposes. In the casing l openings are provided for, the insertion of the ends of the holding clip.

Supported in the base of the casing are two L- shaped pole pieces 9. These consist of a vertical arm III and a horizontal arm II. The latter is drilled .formounting the pole pieces on pillars l2. These pillars extend through the inset casing .2 and the magnetic disc I and are secured in the base 0! the casing I, a collar on the pillar 2. Located between the pole pieces is the bar magnet I3 which may be of magnetic material strongly resistant to self-demagnetisation such as that known under the trade-mark Alnico." This material has a high coercivitys This magnet is a rectangular block and extends between the pole pieces in close contact therewith. The pole pieces are providedwlth projections H which extend beyond the barmagnet and are drilled to provide support for posts I! whichv extend therebetween. The upper post Fig. 1 is tapped for the insertion of a screw carrying a bracket member I6. This latwhich may be a rectangular block of the same shape as the bar magnet It. This bar magnet I1 is held rigidly between the bracket over the top 0! the magnet and the inset casing 2 at the bottom of the magnet. The magnetic ring 6 provides extra support at the sides of the magnet. The post I! in the lower half of Fig. l is tappedifor the attachment of a strain cord bracket l8. This is provided for the attachthrough the openment of the cord which comes I between the casing l and a fur The pillars I! also serve as supports for terminal brackets it. These terminals which are mounted so as to be insulated from the pillar I! are prevented from rotating about the pillar by means of downturned flaps 2| whichare inserted in raised insulating pillars 2| forming part of the casing I. The terminal brackets II are connected to the respective coils by means 01 the wires 22. These coils II are the usualexciting coils.

The direction or magnetisation' in the permitnent magnet l3 and the shielding magnet l| are t so arranged that stray magnetic held from the permanent magnet is taken up by the shielding magnet. In this way a very efllcient method of eliminating or reducing to negligible dimensions the stray magnetic ileld of a receiver has achieved.

I claim? I 1.- A' telephone receiver comprising a a. diaphra m. pole pieces adiacentthe diaphragm; a permanent magnet clamped between. said poles,

but in opposition to the first magnet. and a thin metallic shield surrounding said magnets for retaining the influence thereo! within the shield.

2. In a telephone receiver having a diaphragm and the usuaipermanentmagnet structure for operating the diaphragm, a c'asing of insulation enclosing said structure, a light metallic non magnetic lining for said casing, a thin shell of magnetic material oi tubular shape inside the lining encircling the structure, and a disc of magnetic material inthe bottom of the casing coverhis one end of the tubular shaped shell.

' 3;Affltelephdnereceiver comprising a diaphragm, pole pieces adjacent said diaphragm, a permanent magnetclamped between said pole pieces, a support secured to said pole pieces, and

a second permanent magnet secured to said support in a position parallel to but in opposition to a second permanent magnet arranged to j saidflrst magnetwand adjacent saidpole pieces, and'a shield ior retainingthe influence 01 said magnets therewithin.

rmirrfrron'ron ROSEBY. 

